An active matrix substrate included in a display panel, such as a liquid crystal display panel etc., includes interconnects for display, such as a plurality of gate lines extending in parallel to each other, a plurality of source lines extending in parallel to each other in a direction perpendicular to the gate lines, etc.
For the active matrix substrate, an interconnection structure has in recent years been proposed in which a copper interconnect, which has a lower electrical resistance than that of a conventional aluminum interconnect, is used as the display interconnect, similar to semiconductor devices.
Here, in a liquid crystal display panel including the active matrix substrate employing the copper interconnect, because the copper interconnect has a relatively low electrical resistance as described above, the interconnection structure employing the copper interconnect can contribute to an increase in size and resolution, double-speed drive display, a reduction in power consumption, etc. of the liquid crystal display panel. However, copper in the copper interconnect is likely to diffuse into an amorphous silicon film or a silicon oxide film during the manufacturing process or the operation in high-temperature and high-humidity atmosphere. Therefore, for example, the following problems arise: if copper diffuses into the back channel of a TFT, the threshold voltage (Vth) of the TFT may be changed; and if copper diffuses into a liquid crystal material, the liquid crystal material deteriorates.
For example, PATENT DOCUMENT 1 describes a display device in which, in an electrode layer used in a display element, the concentration of an ionic impurity contaminating a liquid crystal material, a light emitting material, etc. of the display element is reduced to 100 ppm or less.